Photoelectric sensors may be employed to detect objects within a field of view. In some examples, a photoelectric sensor system may be used to discover the absence or presence of an obstruction by employing a light emitting diode (LED) and a photo-detector. Photoelectric sensors are widely used in applications that may include, but are not limited to, manufacturing and consumer applications. Several different types of photoelectric sensor systems may be used, for example, in industrial or commercial settings. One type is retro-reflective.
In a retro-reflective sensor system, an emitter sends a transmitted beam of light across a protected area. The beam, when not obstructed, is designed to hit, and reflect off from, a retro-reflector. The reflected beam then makes its way back to the sensor, where a photo-detector is struck by the reflected beam.
The effective range of a retro-reflective system is limited in part by reflections of the emitted light beams from an object that obstructs the field of view between the emitter and the retro-reflector such as other reflective materials which can also reflect sufficient light beams capable of striking the photoelectric sensor and incorrectly determine that no obstruction is present, when in fact an obstruction is present. For example, white labels on boxes or reflective clothing worn by individuals crossing through the field of view can create a false sensing event. In an illustrative example, retro-reflective systems may be calibrated by introducing a “white card” test sample into the beam, as an obstruction at close proximity to the emitter. If the photoelectric sensor is struck by sufficient scattered light beams to incorrectly determine no obstruction is present, the minimum sensor threshold of the emitter must be increased. Doing so will not only reduce the chance of incorrectly determining no object is present but will also decrease the total detection effective range with which the retro-reflector may be positioned from the emitter to obtain a reliable signal intensity to strike the photoelectric sensor, under normal operating conditions.